1. Field of the invention
This invention relates to a track ball coordinate data inputting device which is used as an external inputting device to simplify an operation of inputting or specifying data on X-Y coordinate positions, and to achieve the operation with high accuracy.
2. Related Art
A conventional track ball coordinate data inputting device is designed as shown in FIGS. 1 and 2 (hereinafter referred to merely as "a track ball unit", when applicable). That is, the track ball unit 1 includes: a coordinate data inputting ball 3 which appears partially in the upper surface of a frame 2; an annular retainer 15 detachably coupled to the frame 2 to prevent the ball 3 from coming off the frame 2; a pair of drivers 4 and 5 provided in the frame 2 in such a manner that they abut with the ball 3 in two directions forming right angles; and two detecting sections 6 and 7 adapted to detect the amount of rotation of the ball 3 as X-Y coordinate data through the drivers 4 and 5.
Those detecting sections 6 and 7 are provided in the frame 2, and connected to a printed circuit board (not shown) having a predetermined conducting pattern. On the printed circuit board are mounted, for instance, micro-switches, which are operated through push buttons on the upper lid of the frame 2, to determine or cancel coordinate positions.
The ball 3 is accommodated in an accommodating section 8a which is formed in a frame member 8 at the center in such a manner that it is circular in section and opened upwardly. In addition, in order to rotatably support the ball 3 floating in the accommodating section 8a, a plurality of supporting spherical elements 9 (five supporting spherical elements 9 in the case of FIGS. 1 and 2) are rotatably held in the spherical inner surface of the accommodating section 8 while being partially exposed.
That is, the ball 3 is not in contact with the spherical inner surface and the retainer 15; more specifically, the ball 3 is in point contact with the supporting spherical elements 9. Hence, the ball 3 can be rotated considerably readily.
With the track ball unit 1, the direction of rotation and the amount of rotation of the ball 3 are detected by the detecting sections 6 and 7 with the aid of the drivers 4 and 5. The output detection signals of the detecting sections 6 and 7 are applied through a cable or the like to a personal computer, so that the cursor is moved on the screen of the display unit of the personal computer. Under this condition, an inputting button on the frame 2 is operated to determine the position of the cursor or to cancel it.
In the track ball unit 1, the ball 3 is rotatably abutted against the drivers 4 and 5 as follows:
The pair of drivers 4 and 5 are each rotatably mounted on the upper ends of bearing parts 13 and 14 which are vertically extended from the frame member 8 of synthetic resin, and their lower end portions are swingably engaged through bearings 11a and 12a with the swing end portions of swingable levers 11 and 12.
This construction will be described with reference to the driver 5 since the drivers 4 and 5 are identical with each other. As shown in FIG. 1, a tension spring 12c is provided on one side of the lever 12. More specifically, one end of the tension spring 12c is connected to the upper end of the lever 12, and the other end is connected to the frame member 8, so that the driver 5 coupled to the swing end portion of the lever 12 is kept urged towards the ball 3 at all times.
The driver 5 is mounted on a rotary shaft 5a. An encoder 7a forming the detecting section 7 is mounted on one end of the rotary shaft 5a. The encoder 7a is in the form of a disk having a number of radial slits. Hence, the rotational displacement of the ball 3 is detected, for instance, as rotational motion in Y-coordinates.
In the above-described conventional track ball coordinate data inputting device 1, the lever 12, the driver 5, the encoder 7a, the ball 3, etc. are arranged as shown simply in FIG. 2. As is apparent from FIG. 2, the rotary shafts 12a of the lever 12 are positioned opposed to the driver 5 and the encoder 7a mounted on the rotary shaft 5a of the driver 5, so that the lever 12, the driver 5, and the encoder 7a are swung back and forth about the common axis of the bearings 12a showing an amplitude corresponding to the eccentricity of the driver 5 from the rotary shaft 5a.
The encoder 7a forming the detecting section 7 is provided farthest from the rotary shafts 12a of the lever 12; that is, it is provided at a position where the above-described swing motion is largest in amplitude. Hence, the eccentric rotation of the driver 5 affects the encoder 7a directly; that is, the encoder 7a is greatly shifted from a photosenser comprising a light emitting section and a light receiving section, which are confronted through the encoder 7a with each other. Therefore, the amount of rotation of the ball 3 is not correct when detected. That is, the conventional track ball unit is low in reliability.
In the conventional track ball unit, the pair of drivers 4 and 5 for detection of X-coordinates and Y-coordinates are individually supported and separately driven. Hence, their relevant components such as bearing means (for instance 11a and 12a) and energizing means (for instance 12c) also must be provided separately. Accordingly, the number of components concerning the drivers 4 and 5, and a space for provision of those components are increased as much, and the number of manufacturing steps is also increased. Thus, it is difficult to decrease the manufacturing cost of the conventional track ball unit or to miniaturize it.
The conventional track ball unit 1 is operated as follows: That is, it is set on a horizontal surface, and the ball is turned with the finger. If, in the track ball unit 1, the ball 3 is small and light, then the ball 3 may be shifted being floated by pressures applied thereto from the drivers 4 and 5, because as was described above the drivers 4 and 5 are kept urged towards the ball 3, and the ball 3 is spaced from the accommodating section 8a and the retainer 15.
In the case where the track ball unit 1 is set inclined; more specifically in the case where, after being set on the liquid crystal display unit of a notebook type personal computer which unit is swingable with respect to the computer body, the track ball unit is operated with the liquid crystal display unit set raised, the ball may be floated and shifted.
If the ball is floated and shifted in this manner, then the amount of rotation detected is undoubtedly low in accuracy.
When, in the above-described conventional track ball unit 1, signal processing ICs mounted on its printed circuit board 50 is electrostatically charged, for instance, through the operator's hand, the ICs may be erroneously operated or at worst broken. In order to overcome this difficulty, for instance as shown in FIG. 2, an annular copper foil 71 is bonded to the frame 2 in such a manner as to surround the ball 3, and a coil spring 72 is disposed between the copper foil 71 and the printed circuit board 50 provided below the frame 2, so that the copper foil 71 is electrically connected to the grounding part GND of the printed circuit board 50 through the coil spring 72.
In the track ball unit 1, a plurality of components (such as the copper foil 71 and the coil spring 72) are employed to eliminate the above-described electrostatic difficulty. Therefore, the track ball unit 1 is disadvantageous in that it is low in assembling efficiency, and high in manufacturing cost.